1. Field of the Invention
The present invention is in the field of reinforced polysiloxane copolymers. More particularly, the present invention is directed to silica reinforced polysiloxane copolymers which have high optical refractive index and mechanical properties rendering the copolymers eminently suitable for use in intraocular lenses.
2. Brief Description of the Prior Art
Intraocular lenses have been known for a long time. Such lenses are surgically implanted into the human eye to replace damaged or diseased natural lenses of the eye.
Whereas intraocular lenses can be made from "hard" polymeric or glass optical materials, soft resilient polymeric materials comprising polysiloxane polymers or copolymers have been increasingly used in the art for this purpose. U.S. Pat. No. 4,615,702 describes, for example, intraocular lenses made from "silicone polymers" obtained by polymerization of such monomers as octamethyl-cyclotetrasiloxane, octaphenylcyclotetrasiloxane, trimethyltriphenyl-cyclotrisiloxane, and divinyltetramethyldisiloxane.
Intraocular lenses made from silicone polymeric materials are usually deformable, so that for implantation a smaller incision needs to be surgically cut in the eye than for the implantation of "hard" intraocular lenses. In this respect, the size and mechanical characteristics of the silicone polymeric intraocular lenses play an important role. As it will be well understood by those skilled in the art, for successful implantation the lens must have sufficient structural integrity, elasticity and small enough size to permit the folding for insertion through a small incision. After insertion, the lens must, of course, regain its original molded shape.
It will be further understood by those skilled in the art that the thinner is the lens, the easier is the surgical insertion procedure. On the other hand, in order to function as an intraocular lens, the lens material must have sufficient optical refractory power. Consequently, the higher is the optical refractive index of the silicone material, the thinner can be the lens to obtain the same optical refractory power.
Some silicone polymeric materials described in the prior art contain a silica reinforcer finely distributed in the polymeric silicone resin. Usually such reinforcement of the silicone polymeric material with silica is necessary for the polymeric material to attain adequate structural strength to be used as a foldable intraocular lens. Such silica reinforced polymeric silicone resins suitable for use as soft contact or intraocular lenses are described in U.S. Pat. Nos. 3,996,187; 4,615,702; 3,996,189. Additional disclosures relating to polymeric silicone materials or silica reinforcers, which comprise the background of the present invention can be found in U.S. Pat. Nos. 3,341,490; 3,284,406; 3,457,214; and in European Patent Application No. 0110537 filed on Oct. 18, 1983.
Additional disclosures relating to intraocular lenses can be found in U.S. Pat. No. 4,573,998, published UK Patent Application GB 2114315, and in co-pending application for U.S. Pat. Ser. No. 946,703 filed on Dec. 24, 1986 by Reich et. al. which is now U.S. Pat. No. 4,868,251. The latter U.S. Patent application is assigned to one of the co-assignees of the present application.
The prior art intraocular lenses made of silica reinforced silicone copolymers still do not fully satisfy the need for high enough optical refractory power to permit sufficiently thin lens size which in turn would make it possible to surgically implant the lens through a desirably small incision in the eye. In other words, there is still need in the art for reinforced silicone polymeric materials which have sufficiently high optical clarity, refractive index, durometer hardness, tensile strength and related mechanical properties to permit construction of thin foldable intraocular lenses. The present invention satisfies this need.